The primary objective of this project is to utilize a variety of existing data sources by integrating and analyzing them in novel ways to answer key questions related to the long-term effects of mild traumatic brain injury (mTBI) in veterans over time. Although prior studies have found that moderate and severe TBI are associated with a variety of adverse clinical outcomes, the effects of mTBI are less well understood. We propose to build on our past several years of work within The Chronic Effects of Neurotrauma Consortium (CENC - Epidemiology Study) in which we have assembled a very large or ?mega? data repository of nearly 2 million veterans (including all veterans with a TBI diagnosis) that comprises multiple different national synthesized databases. We are extremely well positioned to capitalize on this national resource to continue to maximally study veterans with mTBI. Specifically, we now have the unprecedented ability to follow these veterans prospectively as they are embedded within the VA national care system and we can investigate both the course and outcomes of TBI. We propose to investigate mTBI and its long-term outcomes through four complementary Specific Aims under the three Objectives of LIMBIC. In Objective 1 Aim 1 we propose to maintain, augment, and refine our current repository, including creating and refining new variables associated with TBI. In Objective 2 Aim 1 we will identify subgroups at the greatest risk and resilience for mental health and neurogenerative outcomes after mTBI, including very-early onset dementia. In Objective 2 Aim 2 we propose to examine and elucidate the complex associations between mTBI and comorbidities such as substance abuse, PTSD, etc. In Objective 3 Aim 1 we will develop prognostic models to determine which veterans decline versus sustain/improve after mTBI. Our overall goal is to investigate how mTBI is interwoven with other comorbidities, especially mental health factors, and how these other factors may be synergistic or additive, how mTBI remote adverse outcomes evolve over time and what predicts this evolution. Furthermore, we will translate our findings to develop prognostic models that will guide clinician and researchers toward better care and prevention of mTBI and associated outcomes.